Extended Data Fig. 5: Schematic illustration of the writing principle of volumetric nanoscale ODS and simulations.
From: A 3D nanoscale optical disk memory with petabit capacity
a, Jablonski diagram of 2-isopropylthioxanthone photoinitiators for the explanation of polymerization by two-photon absorption and depolymerization by triplet–triplet absorption. The green arrows indicate the absorption of the two photons, the brown arrow indicates the radiative relaxation of the fluorescence, the blue arrow indicates the radiative relaxation of the phosphorescence, the grey dashed arrow indicates intramolecular vibrational redistribution (IVR), the red arrow indicates triplet–triplet absorption, the yellow arrows indicate intersystem crossing (ISC)/IVR (dashed arrow) or reverse ISC/IVR (solid arrow), and the black arrow indicates radical formation. The energy levels are not to scale. The solid horizontal lines indicate nonvibrational electronic states whereas the dashed horizontal lines indicate vibrationally excited electronic states. b, Principle of dual-beam nanoscale optical writing. A 515-nm femtosecond Gaussian laser beam initiates polymerization in a medium via two-photon absorption, and a 639-nm CW doughnut-shaped laser beam then deactivates locally the polymerization at the periphery of the focus, which reduces the polymerization volume to the subdiffractive level. c, Simulated profiles of photo-polymerization conversion rate versus deactivating intensity in a dual-beam writing process. The threshold was set to 42%, with the area above 42% representing the third state in Fig. 3, and the area below 42% representing the second state in Fig. 3. d and e, Simulated superresolution STED images of a 4 × 4 pattern formed by the 515-nm femtosecond writing laser beam without (d) and with (e) subsequent application of the 639-nm deactivating beam. f, Simulated confocal image of the pattern formed by the dual-beam writing configuration. g, Intensity profiles extracted from (d–f).
